1. Field of the Invention
The present invention relates to an exposure apparatus and an exposure method employed for pattern exposure on a resist film, and more specifically, it relates to an exposure apparatus and an exposure method capable of correctly managing a light exposure.
2. Description of the Prior Art
A photolithographic process consists of an application step, an exposure step and a development step for a resist film. Among these steps, the exposure step is carried out for transferring a pattern image formed on a reticle to a resist film provided on a wafer. In general, a reduced projection exposure system is employed in the exposure step.
The structure of an exposure apparatus employing the reduced projection exposure system is schematically illustrated with reference to FIG. 8. This exposure apparatus comprises a light source 102 emitting an exposure beam 100A, a reflecting mirror 104 reflecting the exposure beam 100A emitted from the light source 102, a beam shaping optical system 106 converting the exposure beam 100A to an exposure beam of a prescribed component, fly-eye lenses 108 and 112 for uniformly illuminating an exposure range, a condenser lens 118 illuminating the overall areas of the reflecting mirror 106, another reflecting mirror 116 and a reticle 120, a reduced projection lens 122 for reducing the pattern of the exposure beam passing through the reticle 120 and projecting the exposure beam to a wafer 124 placed on a stage 126 and a control unit 200 for controlling the light exposure time etc. of the light source 102, the position of the stage 126, information obtained from an illuminance meter 130A described later and other elements of the exposure apparatus.
In the exposure step of forming a pattern on a resist film, the light exposure is generally corrected by providing the illuminance meter 130A on the stage 126 located on the emission side of the reduced projection lens 122 for previously measuring illuminance with the illuminance meter 130A before the exposure step and controlling the light exposure time so that an integrated light exposure (product of the illuminance and the exposure time) in the exposure step is regularly constant on the basis of the obtained illuminance, as shown in FIG. 10. In a step-and-repeat batch exposure method, for example, the exposure time is decided on the basis of the obtained illuminance for controlling the integrated light exposure. In a scan exposure system, the moving speed of the stage 126 is calculated on the basis of the obtained illuminance for controlling the integrated light exposure.
In the aforementioned method of correcting the light exposure, however, the illuminance meter 130A provided on the emission side of the reduced projection lens 122 of the exposure apparatus must be periodically calibrated with another illuminance meter having normal sensitivity, in order to confirm deterioration of sensitivity of or abnormality of the illuminance meter 130A provided on the exposure apparatus.
As the wavelength of the exposure beam employed for the exposure step is reduced, further, illuminance on the emission side of the reduced projection lens 122 is remarkably reduced due to a blur of the reduced projection lens 122 (reduction of transmittance of the reduced projection lens 122 resulting from solarization) along with progress of the number of applied pulses (exposure time) with the reduced projection lens 122, as shown in FIG. 10.
When the exposure apparatus carries out no exposure step for a prescribed time, the surface of the reduced projection lens 122 is so contaminated by organic matter and inorganic matter that the illuminance is disadvantageously reduced on the emission side of the reduced projection lens 122.
A first object of the present invention is to provide an exposure apparatus capable of reducing the number of times of calibration of an illuminance meter provided on the emission side of a reduced projection lens of the exposure apparatus, an exposure method and a semiconductor device fabricated with the exposure method.
A second object of the present invention is to provide an exposure apparatus capable of properly setting a light exposure in consideration of a blur of a reduced projection lens, an exposure method and a semiconductor device fabricated with the exposure method.
A third object of the present invention is to provide an exposure apparatus capable of preventing reduction of illuminance resulting from contamination of the surface of a reduced projection lens by organic matter and inorganic matter.
According to an aspect of the present invention, an exposure apparatus setting a prescribed light exposure in exposure for forming a resist pattern with an optical system comprises at least two illuminance meters provided on the emission side of the aforementioned optical system, an average illuminance operation unit operating average illuminance on the basis of measured illuminance values obtained from the aforementioned illuminance meters, and a light exposure control unit controlling the light exposure on the basis of information obtained from the aforementioned average illuminance operation unit.
According to another aspect of the present invention, an exposure method setting a prescribed light exposure in exposure for forming a resist pattern with an optical system comprises an average illuminance operating step of operating average illuminance on the basis of measured illuminance values obtained from at least two illuminance meters provided on the emission side of the aforementioned optical system and a light exposure control step of controlling the light exposure on the basis of information obtained from the aforementioned average illuminance operating step.
According to the aforementioned exposure apparatus and the aforementioned exposure method, the illuminance meters are so provided in plural that dispersion of measured values or the like is averaged and measurement accuracy for the illuminance can be improved.
In the aforementioned exposure apparatus, the aforementioned average illuminance operation unit preferably includes a unit obtaining the average illuminance with remaining measured illuminance values except those of measured illuminance values exceeding a prescribed threshold in illuminance measurement.
In the aforementioned exposure method, the aforementioned average illuminance operating step preferably includes a step of obtaining the average illuminance with remaining measured illuminance values except those of measured illuminance values exceeding a prescribed threshold in illuminance measurement.
When the prescribed threshold is provided for the measured values for obtaining the average illuminance except the measured values exceeding the threshold, deterioration or abnormal values of the illuminance meters can be omitted so that the number of times of calibration of the illuminance meters provided on the emission side of the reduced projection lens of the exposure apparatus can be reduced as compared with the conventional exposure apparatus.
According to still another aspect of the present invention, an exposure apparatus setting a prescribed light exposure in exposure for forming a resist pattern comprises an illuminance measuring unit performing illuminance measurement before exposing an (Nxe2x88x921)th (N: integer) wafer, illuminance measurement after exposing the (Nxe2x88x921)th wafer and illuminance measurement during at least single exposure of the (Nxe2x88x921)th wafer and a light exposure decision unit deciding illuminance for an N-th wafer from measurement results obtained from the aforementioned illuminance measuring unit for deciding the light exposure for exposing the N-th wafer.
According to a further aspect of the present invention, an exposure method setting a prescribed light exposure in exposure for forming a resist pattern comprises an illuminance measuring step of performing illuminance measurement before exposing an (Nxe2x88x921)th (N: integer) wafer, illuminance measurement after exposing the (Nxe2x88x921)th wafer and illuminance measurement during at least single exposure of the (Nxe2x88x921)th wafer and a light exposure decision step of deciding illuminance for an N-th wafer from measurement results obtained from the aforementioned illuminance measuring step for deciding the light exposure for exposing the N-th wafer.
According to the aforementioned exposure apparatus and the aforementioned exposure method, the exposure time can be correctly set with high precision by deciding the exposure time every shot, also when illuminance on the emission side of the reduced projection lens is reduced following progress of the exposure time of the reduced projection lens due to a blur of the reduced projection lens (reduction of transmittance of the reduced projection lens resulting from solarization) as the wavelength employed for exposure is reduced, dissimilarly to the prior art.
In the aforementioned exposure apparatus, the aforementioned light exposure decision unit preferably includes a relational expression operation unit obtaining a relational expression of illuminance and an exposure time from illuminance measurement results obtained from the aforementioned illuminance measuring unit and a first illuminance operation unit obtaining illuminance at the time of starting exposure of the N-th wafer and illuminance at the time of ending the exposure from the relational expression obtained by the aforementioned relational expression operation unit.
In the aforementioned exposure apparatus, the N-th wafer is further preferably provided with a plurality of shot areas, and the aforementioned light exposure decision unit preferably further includes a second illuminance operation unit obtaining illuminance every shot of the N-th wafer and an exposure time operation unit obtaining an exposure time every shot of the N-th wafer.
In the aforementioned exposure method, the aforementioned light exposure decision step preferably includes a relational expression operation step of obtaining a relational expression of illuminance and an exposure time from illuminance measurement results obtained from the aforementioned illuminance measuring step and a first illuminance operation step of obtaining illuminance at the time of starting exposure of the N-th wafer and illuminance at the time of ending the exposure from the relational expression obtained in the aforementioned relational expression operation step.
In the aforementioned exposure method, the N-th wafer is preferably provided with a plurality of shot areas, and the aforementioned light exposure decision step preferably further includes a second illuminance operation step of obtaining illuminance every shot of the N-th wafer and an exposure time operation step of obtaining an exposure time every shot of the N-th wafer.
In the aforementioned exposure apparatus and the aforementioned exposure method, the exposure time can be correctly set with higher precision.
According to a further aspect of the present invention, an exposure apparatus setting a prescribed light exposure in exposure for forming a resist pattern comprises a dummy exposure unit performing dummy exposure after a lapse of a prescribed time from completion of an exposure step for a wafer to an exposure step for a next wafer.
According to a further aspect of the present invention, an exposure method setting a prescribed light exposure in exposure for forming a resist pattern comprises a dummy exposure step of performing dummy exposure after a lapse of a prescribed time from completion of an exposure step for a wafer to an exposure step for a next wafer.
According to the aforementioned exposure apparatus and the aforementioned exposure apparatus, a blur of the surface of an optical system resulting from contamination by various types of organic matter and inorganic matter is relaxed by a self-cleaning effect due to the dummy exposure, and the optical system can be prevented from a blur resulting from influence by environment.
According to a further aspect of the present invention, a semiconductor device is fabricated with an exposure method comprising an average illuminance operating step of operating average illuminance on the basis of measured illuminance values obtained from at least two illuminance meters provided on the emission side of a single optical system and a light exposure control step of controlling the light exposure on the basis of information obtained from the aforementioned average illuminance operating step.
According to a further aspect of the present invention, a semiconductor device is fabricated with an exposure method, setting a prescribed light exposure in exposure for forming a resist pattern, comprising an illuminance measuring step of performing illuminance measurement before exposing an (Nxe2x88x921)th (N: integer) wafer, illuminance measurement after exposing the (Nxe2x88x921)th wafer and illuminance measurement during at least single exposure of the (Nxe2x88x921)th wafer and a light exposure decision step of deciding illuminance for an N-th wafer from measurement results obtained from the aforementioned illuminance measuring step for deciding the light exposure for exposing the N-th wafer.
According to a further aspect of the present invention, a semiconductor device is fabricated with an exposure method, setting a prescribed light exposure in exposure for forming a resist pattern, comprising a dummy exposure step of performing dummy exposure after a lapse of a prescribed time from completion of an exposure step for a wafer to an exposure step for a next wafer.
In the aforementioned semiconductor device, the pattern is correctly formed on a resist film, whereby the yield can be improved in steps of fabricating the semiconductor device.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.